1. Field of the Invention
This invention is related in general to the field of drive mechanisms. In particular, the invention consists of a reversible ratchet mechanism for propelling a wheelchair through the reciprocating motion of a lever actuated by the occupant of the chair.
2. Description of the Prior Art
Wheelchairs, bicycles, and other types of wheeled vehicles are typically propelled by a user imparting energy through a rotation arc. For example, a bicycle is powered by the rider applying a force that produces a tangential component along the circular path of rotation of the pedals. A wheelchair is hand powered in similar manner by gripping the circular rails attached to the wheels and pushing or pulling, depending on the direction of travel, along an arc of the rail. Because the rails follow the rotation of the wheels, the motion of the user's hands necessarily travel through the arc, which requires a continual change in the direction of application of the force in order to optimize the tangential resultant that provides the rotational motion of the wheels. This unusual motion involves the use of a different group of muscles than is required to push or pull in linear motion. Therefore, it is apparent that a person could apply more force by operating a handle in linear fashion along a straight path. The linear motion of the handle could then be converted to rotational motion in any conventional manner to propel the wheelchair.
Moreover, it has been found that the nonlinear motion associated with the hand propulsion of a wheelchair, transmitted to the arms and shoulders, after prolonged use can have a debilitating effect on the user's muscles, tendons and ligaments in the form of tendonitis, muscle weakness, and even arthritis. Therefore, also for this reason a repetitive linear motion would be highly preferable to the arc motion inherent with the use of a conventional wheelchair. In particular, it would be very desirable to have a device enabling a person to propel a wheelchair by pushing or pulling, depending on the direction of motion, a set of reciprocating levers coupled to the armrests of the chair.
The prior art is replete with devices for driving wheelchairs, bicycles, and other types of wheeled vehicles by applying a force in some manner. In U.S. Pat. No. 5,683,321, Barnett describes a drive apparatus for converting linear motion to rotary motion for continuously transmitting power to an axle, such as in a wheelchair. The drive apparatus consists of a flexible ratch, such as a chain, belt or cable, and first and second energy-transmitting members for releasably engaging the ratch. The energy-transmitting members are moved by hand in reciprocating linear motion along the flexible ratch, which is alternately engaged and driven by one or the other of the energy-transmitting members. Every time the direction of motion is reversed, the engagement of the energy-transmitting members to the ratch is also reversed and the resulting reciprocating linear strokes are converted to unidirectional linear motion, which is then converted to a rotational motion suitable to propel the wheelchair or other device.
The Barnett device, however, does not allow a user to change the direction of the rotational motion without employing a second pair of energy-transmitting members. Moreover, because the flexible ratch is always engaged by one of the members, a significant effort is required while applying force in both directions. Therefore, there is still a need for a reversible mechanism that allows propulsion of a wheelchair by applying force to an actuating lever in linear, reciprocating fashion.